The Seldon Plan guided the First Foundation safely through two centuries of chaos as the Galactic Empire disintegrated. Seldon's recorded holographic image appeared in the Council Chamber on Terminus at moments of crisis predicted by pshychohistory, and his voice was heard. Even war between the Foundation and the remains of the Empire was foreseen - and planned for - by the great scientist. But Seldon had no way of predicting the birth of the Mule, a mutant of uncanny power and unlimited ambition.

The Mule's conquests are effortless and his subjects mind-controlled slaves. The Foundation is powerless against the supernormal force the Mule exerts. The Seldon Plan is in tatters. Two men and a woman from Terminus flee to the ruins of mighty Trantor in an effort to discover where the mysterious Second Foundation was established. Its help is needed desperately against the mental powers of the Mule. But the Mule, using those same astonishing powers, is also looking for the Second Foundation.